It is a scheme, which allows you to cross the border of a given country based on a valid passport, without the necessity of obtaining any visa nor any residence card.
For instance, the Ukrainian citizens who are holders of biometric passports may enter the territory of Poland based on visa-free travel scheme. The conditions of entry and stay, as well as the list of states whose nationals are exempted from a visa requirement when entering the territory of Poland, can be found at the following website:
https://udsc.gov.pl/en/cudzoziemcy/obywatele-panstw-trzecich/chce-przyje....
